The present invention relates to a magnetoresistive effect (MR) sensor used for various magnetic detection, especially utilizing giant magnetoresistive effect (GMR) such as spin valve magnetoresistive effect (SVMR) or utilizing tunneling magnetoresistive effect (TMR), to a thin-film magnetic head used in a-magnetic record and/or reproduction device such as a HDD (Hard Disk Drive) unit, and to a thin-film wafer with a plurality of the thin-film magnetic heads.
Recent growth rate of the recording density in magnetic recording is remarkable, for example, 100% of the average annual growth rate may be achieved. Increasing conversion efficiency in thin-film magnetic heads supports this growth in the recording density. A MR conversion rate of a thin-film magnetic head utilizing an anisotropic magnetoresistive effect (AMR) was merely about 2% at most. Whereas the MR conversion rate of a thin-film magnetic head with a SVMR sensor that is one of GMR sensors exhibiting high sensitivity and high power is 6-8%. This is about three times of that of the AMR head.
The SVMR head has a structure with first and second thin-film layers of a ferromagnetic material magnetically separated by a thin-film layer of non-magnetic metallic material, and a layer of anti-ferromagnetic material is formed in physical contact with the second ferromagnetic layer to provide exchange bias magnetic field by exchange coupling at the interface surface of the layers. The magnetization direction in the second ferromagnetic layer is constrained or maintained by the exchange coupling, hereinafter the second layer is called xe2x80x9cpinned layerxe2x80x9d. On the other hand the magnetization direction of the first ferromagnetic layer is free to rotate in response to an externally applied magnetic field, hereinafter the first layer is called xe2x80x9cfree layersxe2x80x9d. The direction of the magnetization in the free layer changes between parallel and anti-parallel against the direction of the magnetization in the pinned layer, and hence the magneto-resistance greatly changes and GMR characteristics are obtained.
The output characteristic of the SVMR head depends upon the angular difference of magnetization between the free and pinned layers. The direction of the magnetization of the free layer is free to rotate in accordance with an external magnetic field. That of the pinned layer is theoretically fixed to a specific direction (called as xe2x80x9cpinned directionsxe2x80x9d) by the exchange coupling between this layer and adjacently formed anti-ferromagnetic layer.
During operation of the SVMR head, it is required that the magnetization direction in the free layer changes without accompanying domain wall movement. This is because the magnetization change accompanied by domain wall movement is non-reciprocal change and responds slower than that accompanied by no domain wall movement, and therefore produces a noise called as Barkhausen noise. Thus, in general, hard magnet layers are arranged at the both end portions of the SVMR structure, for providing bias magnetic field or longitudinal bias to the free layer so as to prevent domain wall movement from occurring.
In such SVMR head, if the magnetization direction in the pinned layer changes in accordance with some externally applied magnetic field, the magnetization direction in the free layer also changes under the influence of this magnetization direction change in the pinned layer so as to vary its output voltage. In fact, a composite type thin-film magnetic head with a SVMR sensor element and an inductive writing element tends to cause two state problems in which the output voltage of the head after writing operation takes two values. It is guessed that such two state problems are caused by change of the magnetization direction in the pinned layer due to applied writing magnetic field from the inductive element.
Since the magnetization direction in the free layer is not completely in parallel with the surface of the magnetic recording medium but inclines toward the magnetic recording medium, the asymmetry characteristics of the SVMR head when it is off-tracked is greatly shifted to the negative side. This inclination is especially large at the track edge regions. If the asymmetry characteristics shifts to the negative side greatly, servo control for controlling the position of the SVMR head to the track center by servo signals recorded on the magnetic recording medium cannot be accurately carried out.
It is therefore an object of the present invention to provide a MR sensor, a thin-film magnetic head and a thin-film wafer with the thin-film magnetic heads, whereby instability of output characteristics such as two state problems can be resolved.
Another object of the present invention is to provide a MR sensor, a thin-film magnetic head and a thin-film wafer with the thin-film magnetic heads, whereby improved asymmetry characteristics can be expected.
According to the present invention, a MR sensor, a thin-film magnetic head and a thin-film wafer with a plurality of the thin-film magnetic heads has a MR multi-layered structure including a non-magnetic material layer, first and second ferromagnetic material layers (free and pinned layers) separated by the non-magnetic material layer, and an anti-ferromagnetic material layer formed adjacent to and in physical contact with one surface of the pinned layer, the one surface being in opposite side of the non-magnetic material layer, the multi-layered structure having ends in a direction parallel to a magnetically sensitive surface or an air bearing surface (ABS), and longitudinal bias means formed at both the ends of the MR multi-layered structure, for providing a longitudinal magnetic bias to the MR multi-layered structure. Particularly, according to the present invention, the MR multi-layered structure is shaped such that a magnetization direction of the pinned layer is inclined an angle from an axis of easy magnetization of the pinned layer.
Since the magnetization direction of the pinned layer forms an angle with respect to the easy axis of the pinned layer, the magnetization direction of the pinned layer becomes easy to return even if external magnetic field is applied thereto. Therefore, instability of output characteristics such as two state problems that will be induced by applied external magnetic field, for example writing magnetic field, can be effectively resolved.
It is preferred that the magnetization direction of the pinned layer is inclined an angle toward a direction opposite to or the same direction as a direction of the longitudinal magnetic bias from the easy axis of the pinned layer.
If the magnetization direction of the pinned layer is inclined an angle of larger than 0 degree from the easy axis of this pinned layer, improved stability of output characteristics may be obtained. In fact, this angle is preferably determined to an angle of equal to or larger than 2 degrees, more preferably to an angle of equal to or larger than 5 degrees. If this angle is too large, the output voltage will decrease. Thus it is preferred that this angle is determined to an angle of equal to or smaller than 60 degrees.
According to the present invention, furthermore, a MR sensor, a thin-film magnetic head and a thin-film wafer with a plurality of the thin-film magnetic heads in which interface surfaces between the MR multi-layered structure of GMR or TMR and the longitudinal bias means are inclined an angle from a direction perpendicular to the magnetically sensitive surface or the ABS. In other words, the end faces in the track-width direction, of the MR multi-layered structure are not perpendicular to the ABS or the magnetically sensitive surface but inclined the angle toward the longitudinal bias means or the track-width direction in case of a magnetic head. Since the end faces of the MR multi-layered structure are inclined, the end faces of the pinned layer also inclined.
Thus, the shape anisotropy of the pinned layer due to the inclination of its end faces and the layer anisotropy of the pinned layer itself of are making an angle, the magnetization direction of the pinned layer becomes easy to return even if external magnetic field is applied thereto. As a result, instability of output characteristics such as two state problems that will be induced by applied external magnetic field, for example writing magnetic field, can be effectively resolved.
Furthermore, the end faces of the MR multi-layered structure are inclined, deviation of the asymmetry characteristics from its center becomes small and as a result correct and accurate servo control can be obtained.
Japanese Unexamined Patent Publication No.8(1996)-18120 discloses a MR element with inclined end edges for controlling the magnetic domain of the MR element into a single domain structure without applying any longitudinal bias. Thus, this conventional art quite differs in objects and in constitutions, as well as operations and advantages from these of the present invention.
Japanese Unexamined Patent Publication No.8(1996)-235534 discloses a thin-film AMR head with a MR layer which includes one outer edge inclined by an obtuse angle with respect to its under edge so as to resolve problems of right and left asymmetry in its off-track sensitivity. Such asymmetrical off-track sensitivity is caused by inclined magnetization of the MR layer in the AMR head turned by 45 degrees against the ABS. In case of the AMR head, since the magnetic field applied from the magnetic recording medium and passing through the MR layer orients perpendicular to the above-mentioned magnetization direction, the off-track sensitivity of the MR layer differs between its right side and left side. Therefore, this conventional art intends to resolve the problems of asymmetrical off-track sensitivity in the MR layer of the AMR head.
As is well known, the theory of operations of GMR and TMR heads and also the magnetization in the GMR and TMR elements themselves completely differ from these of the AMR head. Especially, in the GMR or TMR multi-layered structure of the GMR or TMR head as the magnetic head according to the present invention, since the magnetization direction of the free layer is almost parallel to the ABS, no asymmetrical sensitivity distribution like the AMR head is produced. Thus, problems to be solved by the present invention is quite different from that of the conventional art described in Japanese Unexamined Patent Publication No.8(1996)-235534. According to the present invention, in order to obtain magnetic stabilization in the pinned layer, the GMR or TMR multi-layered structure is configured so as to incline the magnetization direction of the pinned layer to its easy axis. Thus, this conventional art quite differs in objects and in constitutions, as well as operations and advantages from these of the present invention.
U.S. Pat. No. 5,739,988 discloses a GMR head with lead conductors inclined by 45 degrees in order to obtain the AMR effect in addition to the GMR effect. However, in this conventional art, only the lead conductors are inclined, and therefore this conventional art quite differs in objects and in constitutions, as well as operations and advantages from these of the present invention.
It is preferred that the interface surfaces are inclined an angle toward a direction opposite to or the same direction as a direction of the longitudinal magnetic bias from a direction perpendicular to the ABS or the magnetically sensitive surface.
If the interface surfaces are inclined an angle of larger than 0 degree from the direction perpendicular to the ABS or the magnetically sensitive surface, improved stability of output characteristics may be obtained. In fact, this angle is preferably determined to an angle of equal to or larger than 2 degrees, more preferably to an angle of equal to or larger than 5 degrees. If this angle is too large, the output voltage will decrease. Thus it is preferred that this angle is determined to an angle of equal to or smaller than 60 degrees.
Further objects and advantages of the present invention will be apparent from the following description of the preferred embodiments of the invention as illustrated in the accompanying drawings.